The Recommended Dietary Allowances (RDA) for different age groups reported by the Institute of Medicine in 2005 and the “safe levels” reported by the World Health Organization/Food and Agriculture Organization/United Nations University (WHO/FAO/UNU) in 2007 are based on analysis of available nitrogen balance studies. These reports state the mean protein requirement (EAR) to be 0.65 g of ‘good-quality’ protein per kg body mass per day and that the RDA or safe level of protein intake for both adult men and adult women is 0.83 g of ‘good quality’ protein per kg body mass per day and that the Acceptable Macronutrient Distribution Range (AMDR) for protein is 10-35% of total energy for adults. Though not universally accepted, there is considerable debate regarding the validity of the nitrogen balance approach to the determination of whole body protein requirement indicating that new research and novel research methodologies are necessary to establish whether the protein needs and optimal patterns of protein intake change with advancing age in adults.
It is well accepted that loss of body protein in aging (age-related sarcopenia) is associated with increased morbidity and mortality. The debate centres on whether protein intakes above the RDA have additional benefits for older adults, especially with respect to sarcopenia and osteoporosis. Recent metabolic and epidemiological studies suggest that the current recommendations of protein intake may not be adequate for maintenance of physical function and optimal health in older adults. Indeed, much of the recent evidence supports the contention that lean body mass can be better maintained if an older person consumes dietary protein at a level higher than the general RDA defined above. The RDA for protein from these meta-analyses tends towards higher protein intakes of 1.2 gram per kilogram body mass per day (approximating to 90 g for a 75 kg adult) to be evenly dispersed among the three main eating occasions, i.e. morning (breakfast, 30 g), mid-day (luncheon, 30 g) and evening (dinner, 30 g) meals. Of particular relevance, many of the studies for which protein supplements in the elderly have been used comprised isolates of the milk proteins, whey and casein.
Protein quality is judged by the essential amino acid (EAA) content and, therefore, an ‘ideal’ protein intake would be that which satisfies the daily requirements for EAAs, updated by the Institute of Medicine in 2005. Changes in muscle (lean tissue) mass occur in response to alterations in the balance between protein synthesis and degradation. Measured by post-prandial change in muscle protein synthesis (MPS) and protein breakdown (MPB), MPS increases within the immediate period (3-5 h) following ingestion of protein or AA mixture, the type of protein exerting different patterns and magnitude of stimulation of MPS. Proteins with a high relative EAA composition tend to stimulate MPS with a more consistent, positive effect. Milk proteins, whey and casein, are composed of approximately 50% EAAs and considered ideal proteins in this respect. As specific AA are now known to have unique physiologic effects beyond being constituents of protein that may further enhance MPS and accrual of lean tissue. Leucine is an essential amino acid known to induce a post-prandial increase in MPS. Leucine also acts as an insulin secretagogue. Insulin is seen as ‘permissive’ with respect to MPS, but a negative regulator of MPB, thereby augmenting net protein balance. Taking into account the arguments #1 and #2 above the most recent recommended, per-meal anabolic threshold of dietary protein/amino acid intake for older individuals is 25 to 30 g protein per meal, containing ˜2.5 to 2.8 g leucine.
Muscle protein loss during aging may be partly explained by a decreased ability of ageing muscle to respond appropriately to protein/EAA/leucine intake. This defect mainly results from a decreased response and/or sensitivity of protein synthesis and degradation to leucine, ageing muscle being less responsive to the combined anabolic effect of elevated amino acid and insulin concentrations, mainly because of a reduced responsiveness of ageing skeletal muscle to these stimuli of muscle protein synthesis. Aging is also characterized by low grade inflammation, one of the components implicated in the development of sarcopenia. To this effect, antioxidant supplementation is able to improve the ability of leucine to stimulate protein synthesis in ageing muscle independently of an increase in leucine availability.
Rizzoli et al (INTERNATIONAL CONGRESS SERIES, EXCERPTA MEDICA, Vol. 1297, 1 Mar. 2007) is a review of bone growth in adolescence, and considers protein and calcium effects on the developing adult, and in particular the effects of nutrients on bine mass gain but not bone mass loss.
Kerksick et al (NUTRITION, ELSEVIER INC Vol. 23, No. 9, 2 Aug. 2007) describes a 12 week study of resistance (Rx) training versus no resistance training in which men (Mean age 27) were randomly assigned one of four (non-hydrolysed) milk protein+/−creatine supplements. The results show that RX alone can induce change in lean tissue mass and functional outcome independent of dietary/nutritional intervention. The reported body compositional outcome (Table 5) and change in functional outcome (Table 6) is a result of an interaction between resistance training and nutritional effect on lean tissue mass. Resistance training is unsuitable for many elderly patients.
It is an object of the invention to overcome at least one of the above-referenced problems.